The first of the supposedly low intensity blasts ripped through a toilet at around 10 a.m. at the newly built Platform 10 of the railway station in the heart of the city, killing one person and wounding another.
After an hour, by which time Modi had reached Patna but not the rally ground, four explosions took place inside the Gandhi Maidan, killing four others and causing a lot of panic, police and witnesses said.
The Patna railway station is located two-three kilometres from the Gandhi Maidan.
As smoke billowed at the blast sites, people ran in different directions. Witnesses reported seeing some of the rallyists falling on the ground, bleeding and in pain.
Two more bombs went off just outside the Gandhi Maidan, one near a cinema hall and another close to the Twin Tower building complex. But no one died in these two places.
Bihar's Director General of Police Abhayanand confirmed the five deaths and said all the victims succumbed to their multiple injuries at the Patna Medical College and Hospital.
A doctor at the hospital said eight of the injured were in "very critical condition".
The blasts at the Gandhi Maidan, where Modi later addressed a huge rally of Bharatiya Janata Party supporters, took place even as second rung party leaders were addressing the crowds ahead of Modi's arrival.
Modi's meeting itself passed off peacefully, and the Gujarat chief minister made no reference to the bomb attacks. He, however, asked the BJP activists to disperse peacefully.
Later, Modi said the bomb attacks were "deeply saddening". He appealed for peace and calm.
The bombings triggered alarm bells in New Delhi, where Prime Minister Manmohan Singh telephoned Bihar Chief Minister Nitish Kumar and asked him to order a speedy investigation and punish the guilty.
"The prime minister condemns the blasts which occurred at several places in Patna. He appeals to the people to maintain peace and calm," the Prime Minister Office's said on Twitter.
Minister of State for Home R.P.N. Singh said the attacks were "extremely unfortunate" and pledged to "get to the bottom of this".
He said the central government was in touch with the Bihar government, adding that the National Investigation Agency and National Security Guard had been rushed to Patna.
In Bihar, all political parties including the ruling Janata Dal-United and those in the opposition -- Rashtriya Janata Dal, the Congress and Left parties -- condemned the deaths in the explosions.
Senior Superintendent of Police Manu Maharaj said police recovered two live bombs from the railway station, one of which had a timer meant to go off at around 11 a.m.
After the bombings, police appealed to people, particularly those gathered
for the Modi rally, not to touch suspicious objects.
Nitish Kumar cancelled a trip to Munger district and asked the chief secretary and the police chief to submit a report at the earliest.